Purified form of collodion or nitro-cellulose

Used as embedding medium for tissue requiring special treatment eg. Hard tissues

Advantages: Doesn’t require heat at any stage of processing Has a rubbery consistency which gives support

to hard tissues So possible to cut sections of mixed hard and

soft tissue of even thickness while preserving the relationship of cell layers eg.eye

Difficult to cut thin sections Serial sections are difficult to prepare –

may be partially overcome by double embedding

Celloidin processing is very slow, taking several weeks

Blocks and sections must be stored in 70% alcohol otherwise they may become discoloured,dry and shrunken

Thick celloidin – 8% Medium solution – 4% Thin solution – 2% Celloidin is supplied as celloidin wool,

damped with absolute alcohol This wool is used direct from the

container and dissolved in equal parts of absolute alcohol and ether, making an allowance for the absolute alcohol present in the wool

These solutions, particularly thick solution take time to dissolve

It is preferable to soak shreds in absolute alcohol for 4-5 hours before the addition of ether to decrease the time taken to dissolve the shreds

Solutions of celloidin should be kept in well-stoppered jars to avoid evaporation of the ether-alcohol solvent and to prevent contamination with water vapour

Ether is one of the most highly inflammable materials and care should be taken while handling it.

Similar to celloidin, but cheaper and is supplied as a strong 8% pyroxylin solution

Solutions used are: Thick solution – 16% Medium solution – 8% Thin solution – 4%

Necol blocks are easier to cut than celloidin ones

Thinner sections can also be cut They remain clear and don’t become

cloudy on keeping as in case of celloidin blocks

Time schedule is same as celloidin

Tissues require thorough dehydration Following treatment in successive grades

of alcohol and absolute alcohol (with copper sulphate), the tissue is transferred to a mixture of equal parts of absolute alcohol and ether for 24 hours

This preliminary treatment facilitates permeation by successive celloidin solutions

Size of tissue decides the period needed in each of the celloidin solutions

For tissues less than 10mm thickness: Alcohol-ether mixture – 24hrs 2% celloidin or 4% Necol – 5-7days 4% celloidin or 8% Necol – 5-7days 8% celloidin or 16% Necol – 2-3 days

Following impregnation in the thick solution, tissue is placed in a mould containing 8% celloidin

Mould must be at least 1-1 quarter inches in depth to avoid exposure of the tissue as celloidin contracts on evaporation

Leuchkart’s L pieces cannot be used Glass Petri dishes about 2 inches in depth

with loose-fitting ground-glass lids are useful

Celloidin blocks are hardened by evaporation Its essential to prevent bubbles from being trapped

on the cutting surface of the block Hardening of celloidin to a rubbery consistency is

enough Chloroform vapour may be used to accelerate

hardening When block is sufficiently hardenend, excess

celloidin is trimmed off leaving a margin of a quarter inch all around with exception of surface to be cut

Celloidin block is fixed to a vulcanite fibre or hardwood (teak) block of appropriate size to fit the microtome chuck

Block is then hardenend in 70% alcohol for half an hour before cutting

Celloidin, Necoloidin and low viscosiy nitro-cellulose blocks and sections must be preserved and stored in 70% alcohol

Was devised to overcome the disadvantages of standard method like storing in 70% alcohol , etc

Celloidin or Necoloidin blocks are prepared as described earlier but instead of being fixed to vulcanite blocks, are transferred to Gilson’s mixture, which is equal parts of chloroform and cedarwood oil

Celloidin will become transparent and should be removed and exposed to air until dry

When the block is dry, its fixed to vulcanite block in the usual way

Blocks should be kept in air-tight bottles

Tissue is first impregnated with celloidin and subsequently blocked in paraffin wax

Peterfi’s double-embedding procedure: After dehydration, tissue is transferred to

celloidin-methyl benzoate mixture.bottle is shaken several times daily

Celloidin solution is replaced daily for 2-3 days.on complete impregnation, tissue becomes transparent

Tissue is transferred to benzene and given 2 or 3 changes each of 6 hours

Transfer tissue to paraffin wax and impregnate and embed in usual manner

Sections are cut as are ordinary paraffin sections on any standard microtomes

If sections tend to curl off on sides after floating on water, they should be floated on 90% alcohol which will softern the celloidin without dissolving it